[Patch, mips] Fix compiler abort with -mips32r2 -mips16 -msynci

[Patch, mips] Fix compiler abort with -mips32r2 -mips16 -msynci

[Steve Ellcey]

While working on my favorite mips option (-msynci) I noticed an odd thing.
If I compile with '-mips32 -mips16 -msynci' I got a warning about synci not
being supported but if I compiled with '-mips32r2 -mips16 -msynci' I did not
get a warning, even though -mips16 mode does not support synci.  Furthermore
if I compiled a program that called __builtin___clear_cache with '-mips32r2
-mips16 -msynci', the compiler would abort.

In mips.h we have:

/* ISA includes synci, jr.hb and jalr.hb.  */
#define ISA_HAS_SYNCI ((ISA_MIPS32R2            \
                        || ISA_MIPS64R2)        \
                       && !TARGET_MIPS16)

What I found was that in mips_option_override, where we check this macro
to generate the warning we have this code at the front of the function:

  /* Process flags as though we were generating non-MIPS16 code.  */
  mips_base_mips16 = TARGET_MIPS16;
  target_flags &= ~MASK_MIPS16;

Then later, we check ISA_HAS_SYNCI, but at that point TARGET_MIPS16 is
always false because of the above lines.

I looked at changing ISA_HAS_SYNCI to use target_flag_explicit but that
seems like the wrong thing to do for the use of ISA_HAS_SYNCI in mips.md.
Then I modified the if statement in mips_option_override but that resulted
in the use of 'mips32r2 -mips16 -msynci' giving an odd warning message:

warning: the ‘mips32r2’ architecture does not support the synci instruction

But of course mips32r2 does support synci, it is -mips16 that does not.  So I
added a new if statement with an explicit check against mips_base_mips16 to
give a better warning.

OK to checkin?

Steve Ellcey
sellcey@mips.com



2012-07-17  Steve Ellcey  <sellcey@mips.com>

	* config/mips/mips.c (mips_option_override): Fix check for -mips16
	-msynci combination of flags.


diff --git a/gcc/config/mips/mips.c b/gcc/config/mips/mips.c
index 7356ce5..889cfb5 100644
--- a/gcc/config/mips/mips.c
+++ b/gcc/config/mips/mips.c
@@ -16212,6 +16212,14 @@ mips_option_override (void)
       target_flags &= ~MASK_SYNCI;
     }
 
+  /* ISA_HAS_SYNCI checks TARGET_MIPS16 but that was turned off at the
+     beginning of this function so we need to check mips_base_mips16.  */
+  if (TARGET_SYNCI && mips_base_mips16)
+    {
+      warning (0, "the \'mips16\' ASE does not support the synci instruction");
+      target_flags &= ~MASK_SYNCI;
+    }
+
   /* Only optimize PIC indirect calls if they are actually required.  */
   if (!TARGET_USE_GOT || !TARGET_EXPLICIT_RELOCS)
     target_flags &= ~MASK_RELAX_PIC_CALLS;
 

Re: [Patch, mips] Fix compiler abort with -mips32r2 -mips16 -msynci

[Richard Sandiford]

"Steve Ellcey " <sellcey@mips.com> writes:
> While working on my favorite mips option (-msynci) I noticed an odd thing.
> If I compile with '-mips32 -mips16 -msynci' I got a warning about synci not
> being supported but if I compiled with '-mips32r2 -mips16 -msynci' I did not
> get a warning, even though -mips16 mode does not support synci.  Furthermore
> if I compiled a program that called __builtin___clear_cache with '-mips32r2
> -mips16 -msynci', the compiler would abort.

The abort sounds like the bug here.  It's deliberate that things like
-msynci, -mbranch-likely, etc., are OK with -mips16.  On the one hand,
you could compile with -mips16 but have an __attribute__((nomips16))
function that could benefit from using SYNCI.  On the other, you could
compile without -mips16 but have an __attribute__((mips16)) function
that needs to avoid SYNCI.

-mips16 really just sets the default ISA mode for functions that don't
specify one.  That's why override_options hides mips16ness so early on,
like you say.

Richard

Re: [Patch, mips] Fix compiler abort with -mips32r2 -mips16 -msynci

[Steve Ellcey]

On Wed, 2012-07-18 at 18:30 +0100, Richard Sandiford wrote:

> The abort sounds like the bug here.  It's deliberate that things like
> -msynci, -mbranch-likely, etc., are OK with -mips16.  On the one hand,
> you could compile with -mips16 but have an __attribute__((nomips16))
> function that could benefit from using SYNCI.  On the other, you could
> compile without -mips16 but have an __attribute__((mips16)) function
> that needs to avoid SYNCI.

OK, I think that makes sense.

> -mips16 really just sets the default ISA mode for functions that don't
> specify one.  That's why override_options hides mips16ness so early on,
> like you say.

Ah, I didn't really understand why we were hiding the -mips16 setting,
now I do.

I will see if I can figure out why we abort.  The clear_cache insn in
mips.md looks a bit odd to me, there is the part that is executed when
TARGET_SYNCI is true and then a part that is only executed if
mips_cache_flush_func is defined.  It looks like if
mips_cache_flush_func is not defined then we do nothing and I was
wondering if that is correct or not?  Should mips_cache_flush_func
being NULL be an error?  I am not even sure if you can make it NULL
given that it is given a default value in mips.opt.

My test case is:

void f()
{
  int size = 40;
  char *memory = __builtin_alloca(size);
  __builtin___clear_cache(memory, memory + size);
}


And the abort with -mips32r2 -mips16 -msynci is:

x.c: In function ‘f’:
x.c:6:1: error: unrecognizable insn:
 }
 ^
(jump_insn 22 21 38 2 (set (pc)
        (if_then_else (eq (reg:SI 207)
                (reg/f:SI 196 [ D.1415 ]))
            (label_ref 33)
            (pc))) x.c:5 -1
     (nil)
 -> 33)
x.c:6:1: internal compiler error: in extract_insn, at recog.c:2129
Please submit a full bug report,
with preprocessed source if appropriate.
See <http://gcc.gnu.org/bugs.html> for instructions.


If I can't figure out what is going on I will file a bug report.

Steve Ellcey
sellcey@mips.com

Re: [Patch, mips] Fix compiler abort with -mips32r2 -mips16 -msynci

[Steve Ellcey]

On Wed, 2012-07-18 at 18:30 +0100, Richard Sandiford wrote:

> The abort sounds like the bug here.  It's deliberate that things like
> -msynci, -mbranch-likely, etc., are OK with -mips16.  On the one hand,
> you could compile with -mips16 but have an __attribute__((nomips16))
> function that could benefit from using SYNCI.  On the other, you could
> compile without -mips16 but have an __attribute__((mips16)) function
> that needs to avoid SYNCI.
> 
> -mips16 really just sets the default ISA mode for functions that don't
> specify one.  That's why override_options hides mips16ness so early on,
> like you say.
> 
> Richard

Here is a new patch.  It clears the MASK_SYNCI bit when setting the
MASK_MIPS16 bit in mips_set_mips16_mode.  I did not add any warnings
because I didn't think we wanted a warning every time we compiled a
function in MIPS16 mode when using -msynci.

How does this patch look?

Steve Ellcey
sellcey@mips.com


2012-07-19  Steve Ellcey  <sellcey@mips.com>

	* config/mips/mips.c (mips_set_mips16_mode): Clear SYNCI_MASK in
	MIPS16 mode.


diff --git a/gcc/config/mips/mips.c b/gcc/config/mips/mips.c
index 7356ce5..00360f7 100644
--- a/gcc/config/mips/mips.c
+++ b/gcc/config/mips/mips.c
@@ -15652,6 +15652,9 @@ mips_set_mips16_mode (int mips16_p)
       /* Switch to MIPS16 mode.  */
       target_flags |= MASK_MIPS16;
 
+      /* Turn off SYNCI if it was on, MIPS16 doesn't support it.  */
+      target_flags &= ~MASK_SYNCI;
+
       /* Don't run the scheduler before reload, since it tends to
          increase register pressure.  */
       flag_schedule_insns = 0;

Re: [Patch, mips] Fix compiler abort with -mips32r2 -mips16 -msynci

[Richard Sandiford]

Steve Ellcey <sellcey@mips.com> writes:
> 2012-07-19  Steve Ellcey  <sellcey@mips.com>
>
> 	* config/mips/mips.c (mips_set_mips16_mode): Clear SYNCI_MASK in
> 	MIPS16 mode.

OK, thanks.

Richard